Synthetic antimicrobial agents such as nalidixic acid, piromidic acid, and the like are known as drugs for curing infectious diseases caused by Gram negative microorganisms. They exhibit, however, only deficient effects on intractable diseases such as pseudomoniasis and the like. On the other hand, antimicrobial agents with a stronger antimicrobial activity, such as norfloxacin, ofloxacin, and the like, have been developed and clinically used.
In order for an antimicrobial agent to effectively exhibit its action, the agent must have a strong antimicrobial activity and must be efficiently utilized. The above-mentioned conventional synthetic antimicrobial agents had a defect in that they are insufficiently absorbed, thus achieving only low utilization by living bodies.
In view of such a situation, the present inventors have synthesized a number of quinolone carboxylic acid derivatives and studied their antimicrobial activity and absorption efficiency by living bodies, and found that quinolone carboxylic acid derivatives of the following formula (I) and their salts exhibited excellent antimicrobial activities and superior absorptivity. Such a finding has led to the completion of the present invention.